The present invention relates generally to devices and methods for forming a waveform of a musical tone, voice or other sound on the basis of waveform data read out from a memory, and more particularly to a waveform generating device and method using loop waveforms read out repeatedly. It will be appreciated that the basic principles of the present invention can be applied extensively to every type of equipment, apparatus and methods having the function of generating musical tones, voices or any other sounds, such as automatic musical performance devices, computers, electronic game devices and multimedia-related devices, not to mention electronic musical instruments. Also, let it be assumed that the terms "tone waveform" in this specification are not necessarily limited to a waveform of a musical tone alone but are used in a much broader sense that embraces a waveform of a voice or any other type of sound.
The so-called "waveform memory readout" technique has already been well known, which prestores waveform data (i.e., waveform sample data) coded by a given coding scheme, such as the PCM (Pulse Code Modulation), DPCM (Differential Pulse Code Modulation) or ADPCM (Adaptive Differential Pulse Code Modulation), and then reads out the thus-prestored waveform data at a rate corresponding to a desired tone pitch to thereby form a tone waveform. So far, various types of "waveform memory readout" technique have been proposed and known in the art, most of which are directed to forming a waveform covering from the start to end of a tone. As one specific example of the waveform memory readout" technique, there has been known prestoring waveform data of a complete waveform of a tone covering from the start to end thereof. As another example, there has been known an approach of prestoring waveform data of a complete waveform for an attach portion of a tone presenting relatively complex variations and prestoring a predetermined loop waveform for a sustain portion of a tone presenting not many variations (e.g., Japanese Patent Laid-open Publication No. SHO-59-188697). In the latter approach, the arrangement of storing the loop waveform for the sustain portion can significantly reduce the necessary quantity of the waveform data to be stored, and also the arrangement of repeatedly reading out the stored loop waveform can effectively adjust the sustained time of the tone as desired. In this specification, the terms "loop waveform" are used to refer to a waveform to be read out repeatedly, i.e., in a looped fashion, and the terms "loop-reproduced waveform" are used to refer to a waveform obtained (reproduced) by reading out the loop waveform repeatedly or in a looped fashion.
Also known in the art is a technique using a plurality of loop waveforms to generate a single tone, where the loop waveforms are read out one after another in given sequence and the resultant loop-read-out data of the successive loop waveforms (i.e., loop-reproduced waveforms) are then subjected to cross-fade synthesis for a smooth connection between the individual loop-reproduced waveforms (e.g., Japanese Patent Laid-open Publication No. SHO-62-14696). In this case, the cross-fade synthesis is effected in predetermined cross-fading sections; however, unlike the above-discussed technique of repeatedly reading out just a single simple loop waveform, this technique is not arranged to variably adjust the time lengths of the individual cross-fading sections. Further, in this case, the loop waveforms are used only in the given sequence corresponding to a single tone.
Among various known examples of the technique of compressing the time axis of a sound signal is one disclosed, for example, in Japanese Patent Laid-open Publication No. HEI-1-93795. This laid-open publication discloses that a sound waveform is divided into a "vowel" section and a "consonant" section and a relatively small time-axial compression ratio is set for the consonant section while a relatively great time-axial compression ratio is set for the vowel section. Further, Japanese Patent Laid-open Publication No. HEI-5-274599 discloses that time-axial compression control is performed only for the vowel section with no time-axial compression control performed for the consonant section. But, these known techniques are directed only to data compression of the sound signal; they never take into account articulation (style of rendition) of the sound and have nothing to do with control of the articulation.
However, the conventionally-known tone waveform generating techniques using the loop waveforms are not satisfactory in that they are not suitable for forming tone waveforms rich in expression and are never related to formation of tone waveforms taking "articulation" (style of performance or rendition) of sounds into account, although they can suitably reduce the necessary quantity of waveform data to be stored. In other known techniques of generating a tone waveform using a plurality of cycles of a waveform prestored for non-repeated or non-looped readout (this type of waveform will hereinafter be called a "non-loop" waveform), the prestored plural-cycle waveform itself can be said to be a good-quality tone waveform taking the articulation (style of rendition) of the sound; however, the sound can be reproduced only as indicated by the prestored waveform data, which would unavoidably result in poor controllability and editability.